I’m trying to repair a small 6 volt DC motor

Thread Starter

Another Rob

Joined May 12, 2024
4
Hello!

I have 2 small 6 volt (10-20 amps) motors, similar but not identical, from which I need to get one working and wired. These motors are 60 +/- years old and I’m dealing with old and brittle wire so I’ve had to open the enclosures to try to splice in new leads.

I have a basic understanding of DC motors but there is a difference between these 2 that I don’t understand:

Each motor has 2 coils. In one motor the 2 coils appear to isolated from each other. In the other motor there is a single winding wire that runs between the coils. The motors also differ in the gauge of the winding wire and the number of windings.

Are both of these motor windings correct? What purpose do the differences serve?

I’m already uncomfortable being inside these motors and I don’t want to cause any damage.

Thanks for your help.

Rob
 

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KeithWalker

Joined Jul 10, 2017
3,180
Which part of the motor is the first picture? It shows too little for me to understand it. Is it the field windings and laminations with the armature removed?
The second picture is showing the two field windings and the commutator. It is rare nowadays for a small DC motor to have a field winding. They usually use permanent magnets for the field.
The brushes and commutator are the most likely to cause problems. The brushes wear down They can become displaced form the brush holders. The commutator segments can become worn and the gaps between them can fill with brush material, causing shorts.
The commutator in the second picture appears to be in fairly good shape but it definitely needs cleaning with alcohol and a pencil eraser.
 

Thread Starter

Another Rob

Joined May 12, 2024
4
Sorry, here are more pictures.

Adding another question: the motor is marked 6v 20 10. I’m interpreting that as 20 amp startup and 10 amp constant loads. Would 14 gauge be adequate for a 3 foot run to the power source? (This motor is from a 1951 motorcycle siren.)

I'll need to clean the commutator. And blow out the case to make sure there’s no swarf left inside.

My questions are to try to understand the differences between the motors and to see if I need to make any repairs.

Appreciate the help!

Rob
 

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KeithWalker

Joined Jul 10, 2017
3,180
This motor does have two field windings on a horseshoe shaped core so that the magnetic poles are opposite each other. The difference in gauge will be because one is wired with the two coils in series and the other in parallel.
Both motors look to be in fairly good shape. A clean up and bearing lube should get them both running again as long as the brushes are not worn down too far.
14 gauge wire should be OK for running them but they may run warm if they were designed for intermittent use on a warning device.
 
Last edited:

Thread Starter

Another Rob

Joined May 12, 2024
4
This motor does have two field windings on a horseshoe shaped core so that the magnetic poles are opposite each other. The difference in gauge will be because one is wired with the two coils in series and the other in parallel.
Both motors look to be in fairly good shape. A clean up and bearing lube …
Ah! That would explain the wire running between the coils on one motor.

I think I’m good to go then.

Thanks,

Rob
 

Thread Starter

Another Rob

Joined May 12, 2024
4
Which part of the motor is the first picture? It shows too little for me to understand it. Is it the field windings and laminations with the armature removed?
The second picture is showing the two field windings and the commutator. It is rare nowadays for a small DC motor to have a field winding. They usually use permanent magnets for the field.
The brushes and commutator are the most likely to cause problems. The brushes wear down They can become displaced form the brush holders. The commutator segments can become worn and the gaps between them can fill with brush material, causing shorts.
The commutator in the second picture appears to be in fairly good shape but it definitely needs cleaning with alcohol and a pencil eraser.
I appreciate all of the info!

Thanks,

Rob
 

MaxHeadRoom

Joined Jul 18, 2013
28,829
@Another Rob There are basically two types of DC brushed motors, one has the field coils and the armature all in series across the supply, It possesses very high low rpm torque, typical use was the automotive starter motor.
The other has the armature in parallel with the field coils. AKA a shunt wound motor.
You will notice that the armature has skewed laminations,. This is to achieve a higher degree of smoothness.
Done on either low pole count or older style brushed servo motors.
 
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